The present invention relates to an opening-closing mechanism for use with image forming apparatus such as copying machines and facsimile systems.
Image forming apparatus such as copying machines and facsimile systems are known which are equipped with an openable automatic document feeder (hereinafter referred to as "ADF"). Opening-closing mechanisms for ADFs include those which are easily attachable to and removable from the body of the image forming apparatus.
Such an opening-closing mechanism for ADFs will be described with reference to FIGS. 4 and 5 which are side elevations in section. The opening-closing mechanism 1 comprises a body-side support assembly 2', an ADF-side support portion 3 and a spring member 4.
The body-side support assembly 2' has a frame 20, side walls 22 formed by upwardly bending opposite side portions of the frame 20, a post 23, a pivot 24 and a positioning member 29. The post 23 is provided on the bottom of the frame 20. The ADF 7 is mounted on the body 6 of an image forming apparatus by inserting the post 23 into a mount cavity 61 in the body 6. The pivot 24 is provided on the rear portion of the frame 20 for movably supporting the ADF-side support portion 3. The positioning member 29 is fixed to the frame 20 as projected downward from the front end of the frame by a predetermined length so that when the ADF 7 is closed, the document conveyor belt 72 of the ADF 7 is positioned approximately parallel to the body 6.
The ADF-side support portion 3 is secured to an ADF cover 71 inside thereof and supported by the pivot 24 on the frame 20 to render the ADF 7 openable about the pivot 24. The support portion 3 is biased upward, i.e., in the direction to open the ADF 7, by the spring member 4 which has one end held in a cutout 31 and the other end held to the body-side support assembly 2'. The ADF 7 can be opened by lifting a knob 73 at the front end of the cover 71 with a force F of about 1.5 kg W which is small relative to the weight of the ADF 7.
The spring member 4 comprises a coiled spring 41 and holders 42, 43. The holder 43 on the cover side holds one end of the coiled spring 41 and has a lateral projecting pin 44, by which the holder 43 is retained in the cutout 31. The holder 42 holds the other end of the coiled spring 41 and has a lateral projecting pin 45, by which the holder 42 is held to the support assembly 2'. The coiled spring 41 is held in place as compressed by the holders 42, 43 to bias the ADF-side support portion 3 obliquely upward with the spring force. The force of the spring 41 is so determined that when the ADF 7 is opened, for example, through an angle of 60 to 70 degrees, the force of the spring 41 is in balance with the weight of the ADF 7 to hold the ADF 7 at the opened position with this angle.
With the ADF opening-closing mechanism described above, the coiled spring 41 is given a great force for biasing the ADF 7 obliquely upward so as to minimize the force F required to open the ADF 7 and to diminish the impact to be produced when the ADF 7 is closed under gravity. Accordingly, when the ADF 7 is in its closed state in which the force of the spring 41 is greatest, the cover 71 of the ADF 7 warps as shown in FIG. 6. Consequently, one side of the ADF 7 where the opening-closing mechanism 1 is provided will be raised off the glass platen 62, failing to position the document conveyor belt 72 in parallel to the apparatus body 6. It is then likely that the document will not be transported onto the glass platen 62 properly.
This drawback may be overcome by using an iron plate, aluminum plate or like rigid body for the cover 71, whereas the use of iron plate or the like results in an increased weight, which entails the necessity of giving a greater force to the spring 41 and enhanced rigidity to the entire opening-closing mechanism 1 and the problem of an increased cost.
Further when the ADF 7 is in its closed state, the coiled spring 41 biases the holder 42 obliquely downward, subjecting the post 23 to a counterclockwise moment about the pivot 24. The post 23 is inclined forward with its lower end portion pressed against the rear lower portion of the wall defining the mount cavity 61 and with its upper end portion pressed against the front upper portion of the wall further because the front-rear width of the post 23 is made slightly smaller than the inside diameter of the cavity 61 to render the ADF mountable on the body 6 with ease.
With the post 23 thus inclined forward relative to the ADF 7, the ADF 7 is displaced forward from the apparatus body 6 by being pushed forward, with the result that the document to be transported onto the glass platen 62 of the body 6 is also displaced forward.
This objection may be obviated by fastening the rear side of the post 23 to the rear portion of the cavity-defining wall as with screws, but this requires a cumbersome time-consuming procedure, makes the ADF 7 difficult to mount and remove, and necessitates an increased number of parts including the screws and an increased cost.